It is known that heating fuel consumed by an internal combustion engine during a cold start, particularly fuel comprising alcohol, enables cold starting of the engine at ambient temperatures below fuel vaporization temperatures, and reduces hydrocarbon (HC) and carbon monoxide (CO) emissions. The Society of Automotive Engineers publications entitled Heated Injectors for Ethanol Cold Starts (SAE 2009-01-0615) by Daniel Kabasin et al. and Emission Reduction with Heated Injectors (SAE 2010-01-1265) by Daniel Kabasin et al., the entire contents of each of which are hereby incorporated herein by reference, document the benefits of using heated fuel injectors to enable low ambient cold starting of engines and to reduce engine emissions.
The temperature control of such heated injectors may use an open loop approach that regulates power to a heater element based on extensive empirical testing of output fuel temperatures for various fuel flow rates, ambient temperatures, coolant temperatures, elapsed time from initiation of crank, and estimated fuel flow rates. The open-loop temperature control is supposed to keep the heater element temperature below a maximum failure temperature of the heater element, below a melting temperature of a protective plastic covering the heater element, and below the boiling temperature of the fuel resident in the injector. This open-loop control also considers manufacturing variation of heater resistances and so requires a safety margin in the power applied to the heaters in order to avoid vapor lock or damage due to excessive heating. Consequently, the open-loop approach may result in less than optimal heating of the fuel and/or failed cold starts.
An alternative to open loop control of heated injectors is to incorporate a temperature sensing means in the fuel injector, as disclosed in commonly owned U.S. Pat. No. 8,439,018, the entire disclosure of which is hereby incorporated herein by reference. While this approach can result in improved temperature control, the addition of the temperature sensing means increases the cost and complexity of the injector and its control system.